The present invention relates to maintenance stations for ink jet printing apparatus and is concerned, more particularly, with the sealing of the maintenance station with a printhead in such apparatus, especially when the maintenance station and printhead are not in alignment with each other; i.e.; misaligned in X, Y, or Z directions.
An ink jet printer of the so-called "drop-on-demand" type has at least one printhead from which droplets of ink are directed towards a recording medium. Within the printhead, the ink may be contained in a plurality of channels and energy pulses are used to cause the droplets of ink to be expelled, as required, from orifices at the ends of the channels.
In a thermal ink jet printer, the energy pulses are usually produced by resistors, each located in a respective one of the channels, which are individually addressable by current pulses to heat and vaporize ink in the channels. As voltage is applied across a selected resistor, a vapor bubble grows in that particular channel and ink bulges from the channel orifice. At that stage, the bubble begins to collapse. The ink within the channel retracts and separates from the bulging ink which forms a droplet moving in a direction away from the channel orifice and towards the recording medium. The channel is then re-filled by capillary action, which in turn draws ink from a supply container. Operation of a thermal ink jet printer is described in, for example, U.S. Pat. No. 4,849,774.
One particular form of thermal ink jet printer is described in U.S. Pat. No. 4,638,337. That printer is of the carriage type and has a plurality of printheads, each with its own ink supply cartridge, mounted on a reciprocating carriage. The channel orifices in each printhead are aligned perpendicular to the line of movement of the carriage and a swath of information is printed on the stationary recording medium as the carriage is moved in one direction. The recording medium is then stepped, perpendicular to the line of carriage movement, by a distance equal to the width of the printed swath and the carriage is then moved in the reverse direction to print another swath of information.
It has been recognized that there is a need to maintain the ink ejecting orifices of an ink jet printer, for example, by periodically cleaning the orifices when the printer is in use, and/or by capping the printhead when the printer is out of use or is idle for extended periods. The capping of the printhead is intended to prevent the ink in the printhead from drying out. There is also a need to prime a printhead before use, to ensure that the printhead channels are completely filled with ink and contain no contaminants or air bubbles. Maintenance and/or priming stations for the printheads of various types of ink jet printer are described in, for example, U.S. Pat. Nos. 4,855,764; 4,853,717 and 4,746,938 while the removal of gas from the ink reservoir of a printhead during printing is described in U.S. Pat. No. 4,679,059.
It has been found that the printing operation or the priming operation, which usually involves either forcing or drawing ink through the printhead, can leave drops of ink on the face of the printhead and that, ultimately, there is a build-up of ink residue on the printhead face. That residue can have a deleterious effect on print quality. It has also been found that paper fibers and other foreign material can collect on the printhead face while printing is in progress, and like the ink residue, can also have a deleterious effect on print quality. It has previously been proposed, in U.S. Pat. No. 4,853,717, that a printhead should be moved across a wiper blade at the end of a printing operation so that paper dust and other contaminants are scraped off the orifice plate before the printhead is capped. It has also been proposed, in U.S. Pat. No. 4,746,938, that an ink jet printer should be provided with a washing unit which, at the end of a printing operation, directs water at the face of the printhead to clean the latter before it is capped.
U.S. Pat. No. 4,223,324 to Yamamori et al. discloses a system comprising a writing head consisting of a liquid chamber supplied liquid, a liquid discharge channel through which the liquid is discharged from the liquid chamber, and an air discharge channel through which dry air is ejected simultaneously with the liquid to a writing surface. A humidifier is provided which is operative when a writing head is in a standby position. A closing member is mounted with respect to the air discharge channel to close it when the writing head is in the standby position. The member acts to direct the humidified air through the exit side of the liquid discharge channel to an air outlet channel. The system is provided with a heating arrangement for heating the humidified air to prevent it from condensing in an air passage leading from the humidifier to the writing head when ambient temperature is low.
German Publication No. 3612299 discloses an ink jet printer comprising a protective cap which can be placed over a printing head when the latter is not in use. A protective solution can be introduced to the protective cap to prevent blockages. A tank, partially filled with a water absorbing polymer material is provided for receiving dirty protective solution when it returns from the cap device.
Japanese Publication No. 53-79536 discloses an apparatus comprising a double sealing arrangement consisting of a nozzle surrounded by a small elastic ring and a large elastic ring. A sponge impregnated with liquid is housed in a space between the small and large rings. The housing prevents ink in the ink jet nozzle from evaporating, thereby preventing clogging of the nozzle.
Japanese Publication No. 62-271749 discloses a provision comprising a cavity wall of a sealing means with a recessed part capable of holding a recording liquid. Under a capped condition, the provision prevents ink coagulation at an ink ejecting port.
Japanese Publication No. 54-119238 discloses a device comprising a clogging preventive device. The device consists of a wetting solution tank and a lip packing holder which is secured to the tank. A lip packing, consisting of rubber, is fitted to a free end of the holder, and one end of a sponge body is inserted into a designated hole in the holder. Another end of the sponge is dipped into the wetting solution in the tank. When not printing, a gap between a head and the holder can be hermetically enclosed.
German Publication No. 2519160 discloses an ink jet printer comprised of ink jet nozzles. The nozzles are covered by a liquid-soaked movable pad. The pad is deformable by engagement with a printing head. Furthermore, the pad is connected to a reservoir which is filled with a water repellent.
One problem encountered with prior art maintenance and/or priming stations is that fluid-tight sealing between the stations and the printhead faces containing the droplet ejecting orifices is not accomplished unless the station walls supporting the resilient gaskets are substantially parallel and aligned with the printhead faces. Such an arrangement requires costly high tolerance assemblies and components. The maintenance station of the present invention avoids the need for such high tolerance alignment between the maintenance station and the orifice containing printhead face.